What Made Mazda's Miller-Cycle Engine Unique, And Which Models Had One?

Mazda's Miller-cycle engine was a notable entry in the annals of automotive history, combining variable valve timing with a screw-type supercharger to maximize the brief compression cycle. The most common version of Mazda's Miller-cycle V6 displaced just 2.3 liters but put out 210 horsepower and 210 lb-ft of torque back in 1995; it eventually earned a place on our list of the most unusual Japanese engines ever made.

The Miller cycle keeps the intake valves open longer during the compression stroke versus a conventional Otto-cycle engine. This minimizes the energy required just to move air in and out of the combustion chambers, which is known as "pumping loss." The reduced resistance from air pressure makes it easier for a Miller-cycle engine to compress the fuel-air mixture, and the Miller cycle also generates less heat in the cylinders and produces less NOx during demanding use. Mazda's engineering on this engine was impressive — it produced 91 horsepower per liter of displacement. In comparison, the limited edition 1995 Ford Mustang Cobra R had a 5-liter engine that made 300 horsepower, a ratio of 60 hp per liter of displacement. Miller-cycle engines were commonly much bigger than Mazda's and traditionally used to power locomotives and large ships.

Mazda originally used the Miller-cycle engine in a single luxury model that was badged according to market through 2002, but it illustrated the automaker's innovative spirit. You won't find the Xedos 9/Millenia on our list of the most successful Mazda models ever, but the Miller-cycle engine didn't die with the well-appointed sedan.

Mazda's Miller-cycle engine was given the designation KJ-ZEM and first appeared in the 1993 Xedos 9, which was badged outside Japan as the Millenia. The car was meant to launch Mazda's upscale Amati line, an intended competitor to Toyota's Lexus and Nissan's Infiniti divisions. Unfortunately the mid '90s were a tough time for Mazda and Japan's economy, so the Millenia wound up going it alone at the top of Mazda's regular lineup. The Millenia S earned EPA ratings of 20 mpg in the city and 28 on the highway, decent numbers for a nearly 3,400-pound luxury sedan.

The Millenia S also qualifies as one of the fastest Mazda cars ever made with a top speed of 143 mph. The model lasted through the 2002 model year in the U.S; Mazda then shelved the Miller-cycle format until 2007. That year, Mazda began using a naturally aspirated 1.3-liter Miller-cycle engine for the model known as the Demio in Japan and the Mazda2 elsewhere. The automaker incorporated some elements of the Miller cycle in designing the Skyactiv -G engines that propel its current models, and Volkswagen borrowed the Miller cycle's shortented intake stroke for the 2.0-liter inline-four that powers some 21st-century Tiguans.